The gap between two doses of AstraZeneca-Oxford Covishield vaccine in India has increased from 6 to 8 weeks to 12 to 16 weeks. The National Technical Advisory Group (NTAGI) says the gap in the UK is 12 weeks, which the WHO has also justified. NTAGI says the UK has learned from this experience. In fact, this gap is only 12 weeks in Britain and the European Union has not even suggested increasing it. In some studies it has been said that the longer the interval between the two doses, the greater the benefit.
What does the research say?
Research data from international teams on this vaccine has shown that a 12-week difference between the two doses has more impact. Trials in the United States, Peru and Chile have shown that giving a second dose at intervals of more than four weeks was 79% more effective. Data from other countries showed that giving a second dose after 6 weeks had more effect. In Brazil, Britain and South Africa, the effect of administering the second dose 6-8 weeks later was found to be 59.9%, 63.7% after 9-11 weeks and 82.4% after 12 weeks or more. The study was published in The Lancet in February, but was not peer reviewed. Currently, no study has seen the effect of a second dose after 16 weeks.
Why the need to increase the interval?
According to an Indian Express report, NTAGI’s Dr NK Arora says there is not enough evidence to increase the 8-week gap, especially when there is no vaccine shortage in the country. According to him, this can be beneficial for countries where there is a shortage of vaccines. He said that increasing the interval may increase the risk of infection in between. However, by increasing the interval, more and more people will receive at least the first dose early. It is also seen in some studies whether the two doses can receive different vaccines. Increasing the interval will reveal more concrete information about it.
More lag increases the effect
In February, WHO Chief Scientist Soumya Swaminathan reported that the second dose of AstraZeneca had a greater effect than increasing the interval. He had said that a difference of more than 12 weeks can give an immune boost. According to a study conducted at the Mayo Clinic in Rochester, USA, a single dose of Pfizer or Moderna can also provide up to 80% protection and subsequently reduce the risk of hospitalization for those infected. At the same time, Spain also made a difference of 16 weeks in the first and second doses of AstraZeneca.